Traditionally, Digital Subscriber Line (DSL) networks have been based on Asynchronous Transfer Mode (ATM) technology. ATM is a high-speed cell-based data transmission protocol. A Digital Subscriber Line Access Multiplexer (DSLAM) is a device that takes a number of DSL subscriber lines and concentrates them onto a single ATM line. Today's DSLAM network infrastructure is based on ATM technology between Customer Premises Equipment (CPE) on one side of the DSLAM and a Broadband Remote Access Server (BBRAS) on the other side of the DSLAM.
An ATM layer loop-back capability allows for operations-related information to be inserted at one location along a Virtual Path Connection (VPC) and to be returned or looped-back at a different location. When a customer has a complaint, operators normally execute a loop-back command in the BBRAS for testing the ATM Virtual Circuit towards the CPE. The CPE answers back with a loop-back signal. This test verifies the physical link between the CPE and the BBRAS. The bases for this functionality are described in ITU-T I.610, which is incorporated by reference herein.
DSLAM products have recently been launched based on Ethernet DSL technology. Instead of communicating mutually via only one transmission media, network nodes may mutually communicate via more than one transmission media. This creates a problem, however, in testing the connection between the CPE and the BBRAS. Operators, of course, desire to have the same testing functionality as they have in their existing DSL network in which ATM is used all the way from the CPE to the BBRAS. By adding Ethernet into the broadband network, however, the standard testing method is limited to the part of the connection between the DSLAM and the CPE (i.e., where ATM is used). A full verification of the connection between the CPE and the broadband network, which is based partly on ATM technology and partly on switched Ethernet, cannot be executed in the operator's network according to standard practice.